Question

must has no past tense. when we want to express the same idea in the past we use

Answer 1

To express the same idea in the past tense you might use " I HAD GOT TO "

EX:

You MUST do your homework.
You HAD GOT TO do your homework.

You MUST go to talk to her .
You HAD GOT TO talk to her.

You MUST pay attention to what I am saying to you .
You HAD GOT TO pay attention to what I am saying to you.

Answer 2

Must has no past tense. when we want to express the same idea in the past we use HAVE TO

We had to go there.
Did we have to go there?
We didn't have to go there.